Followers of our work will recall the merchant vessel SSL Kolkata that was being towed by the Indian Navy after catching fire on June 13th off the Sundarbans in the Bay of Bengal. The Indian Navy had to abandon the ship after a series of explosions and it has been stuck in shallow water ever since. There have been concerns that the 400 tonnes of heavy fuel oil might start leaking as the ship is listing and cracks are developing. The Sundarbans are the world’s largest collection of mangrove forests and a Unesco World Heritage site (https://whc.unesco.org/en/list/452), and a major oil spill here could be devastating. We see indications in this Sentinel 1 radar satellite image from July 17 that this is a legitimate concern: there appears to be a 17km slick coming from the vessel, being pushed by the strong currents from the Ganges Delta.

Sentinel 1 imagery showing a slick visible with Synthetic Aperture Radar that appears to be emanating from the stricken vessel on July 17.

Considering the volume of oil onboard, the slick on July 17 is far smaller than what we would expect if there were a serious leak. This Sentinel 2 multispectral image from the 19th has also captured the slick. Though it doesn’t give us a complete image of the slick as a radar image would (due to interference from the clouds and cloud shadows), we do get an idea of how the slick is spreading not just south, but also north toward the Delta.

Oil slicks seen in Sentinel 2 imagery taken two days later on July 19.

Attempts have been made to salvage the ship but were abandoned after cracks developed and the ship started listing. Now that the fuel tank is underwater, they will need to suck the oil out carefully using a method known as “hot tapping.”Although poor weather has delayed these plans, we have observed one tugboat, the Lewek Harrier, visiting the site as recently as the 19th according to its Automatic Identification System (AIS) signal. Though we couldn’t definitively identify the vessel visible in this image at the time it was collected, the Lewek Harrier was the only vessel that was broadcasting AIS in the area on that day. The MCS Elly II has also been operating in the area though we haven’t seen it in any images.

[ Image 3 ]

This vigilant tug, the Lewek Harrier, has been a regular visitor.

We hope this means an end to this leak and that the extent of the spill will be limited. We will continue to watch this area closely as there is still a real threat to the nearby Sundarbans.

While scanning the European Space Agency’s (ESA) Sentinel-2 satellite images for signs of the Sanchi oil slick, I came across an unusual sight of what appeared to be three, brightly-colored aircraft flying in tight formation. I’m not enough of a GIS rookie to be fooled into thinking China’s latest stealth jets were malfunctioning, what I was observing was a single aircraft’s image split into three spectral bands of red, green, and blue.

This flight was snapped by Sentinel-2 on its way to Tokyo (flight data from Flightradar24.com).

To explain why this happens, we need to take a look at the source of these images: Sentinel-2’s MultiSpectral Instrument (MSI) sensor. This can be thought of as a very advanced camera that can see beyond the usual visual spectrum and into the near-infrared (great for monitoring vegetation) and shortwave infrared. Instead of just one sensor in a camera, the MSI sensor has 12 in a row. For a more technical explanation, take a look at ESA’s guide on the MSI sensor here. Imagine a push-broom with 12, wide bristles and you’ll have an idea of how these sensors sweep across the Earth as the satellite flies overhead. Each sensor splits the image into 10 different spectral bands using a stripe filter which means not only is each band detected at a slightly different angle, they are also detected at slightly different times. What this means for an image like the one above, a “true color” composite made up of the MSI’s red, green, and blue bands, is that when the bands are combined, an assumption has to be made about how far away the object is to correct for the parallax and “focus” the image on the target — and for earth-observation systems like Sentinel, the target is the surface of the earth. An element of parallax is factored in when we combine the bands in the same way that our brains adjust for the parallax of the different angles our eyeballs are seeing. This is called orthorectification. For an example of this, hold your finger halfway between this screen and your face and focus on these words. As well as being a bit blurry, you should be seeing more than one finger. In the same way, the RGB bands are combined with the focus on the surface of the Earth so an aircraft at a higher altitude splits into three images, one for each band. Since this Airbus A321 was cruising at an altitude of about 33,000 feet, the aircraft’s position was projected onto the Earth’s surface resulting in three different images, one for each of the bands.

The time difference between when each band is detected also adds to the offset. This isn’t noticeable for stationary or slow-moving objects but an aircraft is moving fast enough to see a difference. In the image we found, the aircraft’s speed, about 550kts (according to Flightradar24.com), is probably the biggest cause of the shift between images but if you look closely at the contrails, you can see some sideways drift between the first and last image of the plane. The image below, from just off the east coast of Bulgaria, better highlights the two effects of the forward motion of the aircraft and the sideways shift due to parallax.

Example of parallax off the east coast of Bulgaria.

If we really wanted to fix the aircraft’s image, we would need to adjust for the parallax at that distance as well as the delay between each band’s detection (to account for the aircraft’s speed). The result would be that the aircraft would now be one, complete image but everything else would be a multicolor mess.

For more info on this effect, check out this post by Tyler Erickson, or some direct information from the European Space Agency(skip to chapter 2.5).

Together with partners from around the world, SkyTruth uses the view from space to motivate people to protect the environment. SkyTruth is committed to transparency in all things. In the spirit of that, we wanted to share our annual report with you which covers the impact we’ve been able to have as a watchdog, innovator, and motivator for environmental good.

The wasteful practice of flaring off natural gas from oil and gas fields is again making news, coinciding with a new release of SkyTruth’s Global Flaring Map that visualizes gas flaring activity around the globe. This map relies on the Nightfire data provided by NOAA’s Earth Observation Group, which has written extensively about their work detecting and characterizing sub-pixel hot sources using multispectral data collected globally, each night, by the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the Suomi-NPP satellite. Read about the algorithm that creates Nightfire data here and methods for estimating flared gas volumes here.

Date range selection helps you limit the visualization to the time-frame of interest.

You can identify your rectangular Area of Interest and download flaring data within that AOI (works best in Chrome browsers).

We’ve caught up with NOAA’s daily download after adjusting to recent changes in their web security.

About our Global Flaring Map

Please read about some of the uses for this map and how SkyTruth processes NOAA’s data in this original post describing our map. If you don’t see a flaring detection you expected to see, consider the caveats: some flares don’t burn hot enough to be included in our dataset, they may not have been burning when the satellite passed overhead, the flare may not be frequent enough to make it past the 3 detection threshold, heavy clouds may have obscured the flare from the sensor, etc.

If you find this map useful, drop us an email at info@skytruth.org to let us know.

Despite the Senate’s action to keep the methane rule, the Environmental Protection Agency just announced (as of 6/15/2017) they would suspend implementation of the rule for 90 days — an action leading environmental groups claim is unlawful.

Our collaboration with Global Fishing Watch on the problem of transshipment at sea in the fishing industry is at the forefront of a growing movement to take a critical look at this practice, which is increasingly regarded as a key driver of overfishing, and an enabler of illegal fishing and other fisheries crime including crew enslavement. Our work is funded by the Walton Family Foundation and being led by Bay-area skytruthers Aaron Roan and Nate Miller.

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